We are extending our steady state tryptophan fluorescence groundwork on GTP binding protein alpha subunits (40 kDa) that contain 2 Trp/molecule, each in different domains. At least one Trp is important to function and increases in quantum yield by 5-fold when GTP replaces GDP with protein activation. Frequency domain work suggests that a ?s lifetime component is modulated by protein activation. We are mapping the identities of these states using lifetime, anisotropy and quenching dynamic methods to understand the protein refolding that produces function.